Water heaters having internal electric resistance heating elements are well-known and in common use both domestically and commercially. Conventional designs of this type typically consist of a water tank into which cold water is introduced near its bottom, and water heated by the elements is removed from its top. The heating elements are usually in the form of two metallic sheathed electric resistance heating elements of the Calrod .RTM. type which extend into the tank from its inner sidewall and are fully exposed to the water in the tank.
Circulation of water inside the tank is normally very poor. This causes "layering" or layers of significantly cooler water to develop immediately below each element. The effect of layering on overall heating efficiency is two-fold. First, it impedes heat transfer from the elements to the water in the tank, which affects the heater's recovery rate in an undesirable manner. Second, to a certain extent, layering reduces the effective hot water holding capacity of the heater.
As a person skilled in the art would know, water heater recovery rate is directly related to a water heater's capacity to heat an amount of cold water introduced into the tank in response to removal of heated water. In order to overcome this heating inefficiency, I invented a thermosiphon apparatus readily adaptable to conventional water heater designs as shown in my U.S. Pat. No. 4,777,347. However, because the efficiency of water heaters and water heater construction is typically regulated by state standards, many water heater manufacturers were unwilling to modify their tanks in order to implement my thermosiphon apparatus. Therefore, there is a need for a thermosiphon apparatus that improves the efficiency of existing water heaters without involving modifications to the existing water heater tanks by the manufacturers.